Straddled vehicle

ABSTRACT

A straddled vehicle, including: an engine, which includes a combustion chamber; a three-way catalyst, which is configured to purify exhaust gas exhausted from the combustion chamber; an upstream oxygen sensor, which is provided upstream of the three-way catalyst in a flow direction of the exhaust gas, and is configured to detect an oxygen concentration in the exhaust gas; a downstream oxygen sensor, which is provided downstream of the three-way catalyst in the flow direction of the exhaust gas, and is configured to detect the oxygen concentration in the exhaust gas; and a controller, which includes a processor, and a non-transitory storage medium containing program instructions, execution of which by the processor causes the controller to execute a detachment determination process of determining whether the three-way catalyst is detached at least based on a signal input as a signal of the downstream oxygen sensor.

TECHNICAL FIELD

The present teaching relates to a straddled vehicle.

BACKGROUND ART

A straddled vehicle including a three-way catalyst configured to purify exhaust gas has been known. The straddled vehicle indicates all types of vehicles on which a rider rides in a manner of straddling a saddle.

SUMMARY OF INVENTION Technical Problem

The three-way catalyst of the straddled vehicle may be detached by a user. In such a case, the straddled vehicle may run without having the three-way catalyst. It has been demanded to detect that a three-way catalyst has been detached from the straddled vehicle.

An object of the present teaching is to provide a straddled vehicle which is capable of detecting that a three-way catalyst has been detached from the straddled vehicle.

It is noted that the present invention is collective term of a first invention, a second invention, and a third invention that will be described later.

Solution to Problem

(1-1) The straddled vehicle of the first invention is arranged as described below.

The straddled vehicle comprises: an engine which includes a combustion chamber; a three-way catalyst which is configured to purify exhaust gas exhausted from the combustion chamber; an upstream oxygen sensor which is provided upstream of the three-way catalyst in a flow direction of the exhaust gas and is configured to detect oxygen concentration in the exhaust gas; a downstream oxygen sensor which is provided downstream of the three-way catalyst in the flow direction of the exhaust gas and is configured to detect oxygen concentration in the exhaust gas; and a controller which is configured to execute a detachment determination process of determining whether the three-way catalyst has been detached based on a signal input as a signal of the downstream oxygen sensor.

In this specification, the signal input as the signal of the downstream oxygen sensor may be an actual signal of the downstream oxygen sensor input to the controller when the downstream oxygen sensor is connected to the controller. Alternatively, the signal may be a signal input to the controller as a signal of the downstream oxygen sensor when the downstream oxygen sensor is not connected to the controller because, for example, the downstream oxygen sensor is detached or disconnection has occurred between the downstream oxygen sensor and the controller.

In the specification, a phrase “determination based on a signal input as a signal of the downstream oxygen sensor” does not exclude determination based on both a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor. The same applies to a phrase “determination based on a signal of the downstream oxygen sensor”.

In the first invention, the upstream oxygen detector may be an O2 sensor configured to detect whether the oxygen concentration is higher than a predetermined value or not. In the first invention, the upstream oxygen sensor may be an A/F sensor which is configured to output a linear detection signal corresponding to the oxygen concentration. The A/F sensor is configured to continuously detect changes of the oxygen concentration. In the first invention, the downstream oxygen sensor may be an O2 sensor or an A/F sensor. The O2 sensor is configured to output a signal at a first voltage when the oxygen concentration is lower than a predetermined value, and to output a signal at a second voltage when the oxygen concentration is higher than the predetermined value. When both of the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors, the predetermined value of the upstream oxygen sensor and the predetermined value of the downstream oxygen sensor may be identical with each other or different from each other. When the upstream oxygen sensor is an O2 sensor, the upstream oxygen sensor detects whether the air-fuel ratio of air-fuel mixture of air and fuel is higher than a predetermined air-fuel ratio, in terms of the rate of fuel. In this description, when the air-fuel ratio of air-fuel mixture is higher than a predetermined air-fuel ratio in terms of the rate of fuel, the air-fuel ratio is rich. When the air-fuel ratio of air-fuel mixture is lower than the predetermined air-fuel ratio in terms of the rate of fuel, the air-fuel ratio is lean. The predetermined air-fuel ratio is basically a window of air-fuel ratios encompassing the stoichiometric air-fuel ratio, but may be a window of air-fuel ratios which encompasses an air-fuel ratio close to the stoichiometric air-fuel ratio but does not encompass the stoichiometric air-fuel ratio.

(1-2) The straddled vehicle of an embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on both a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor.

(1-3) In addition to the arrangement (1-2) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller is configured to perform feedback control of controlling a fuel supply amount supplied to the combustion chamber based on the signal of the upstream oxygen sensor. The feedback control includes first feedback control which is normal feedback control and second feedback control different from the first feedback control. The controller executes a detachment determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the second feedback control is in execution.

With this arrangement, the precision of determination in the detachment determination process can be easily improved as compared to a case where the signal of the upstream oxygen sensor and the signal of the downstream oxygen sensor while the normal feedback control is in execution are used for the detachment determination process.

In the feedback control, the controller controls the fuel supply amount so that the air-fuel ratio of air-fuel mixture in a combustion chamber alternately switches between rich and lean. Therefore, while the feedback control is being performed, the fuel supply amount periodically increases and decreases. For example, the controller performs the feedback control in such a way that the fuel supply amount is decreased when the first voltage (signal indicating the rich) is input to the controller as a signal of the upstream oxygen sensor and the fuel supply amount is increased when the second voltage (signal indicating the lean) is input to the controller as a signal of the upstream oxygen sensor.

The second feedback control is different from the first feedback control in terms of the cycle and/or amplitude of increase and decrease of the fuel supply amount. The first and second feedback controls may be different from each other in terms of both the cycle and amplitude, only in terms of the cycle, or only in terms of the amplitude. When the first and second feedback controls are different in terms of the cycle of increase and decrease of the fuel supply amount, the cycle of increase and decrease of the fuel supply amount in the second feedback control is longer than the cycle of increase and decrease of the fuel amount in the first feedback control. When the first and second feedback controls are different in terms of the amplitude, the amplitude of increase and decrease of the fuel supply amount in the second feedback control is larger than the amplitude of increase and decrease of the fuel supply amount in the first feedback control.

When the downstream oxygen sensor is an O2 sensor, in the second feedback control, the controller controls the fuel supply amount supplied to the combustion chamber so that a change of the signal of the downstream oxygen sensor occurs. To be more specific, the fuel supply amount is controlled so that the cycle and/or amplitude of increase and decrease of the fuel supply amount is larger than the cycle and/or amplitude in the first feedback control. When the cycle and/or amplitude of increase and decrease of the fuel supply amount is increased, for example, the controller may increase a time until the fuel supply amount starts to decrease after the first voltage is input to the controller and a time until the fuel supply amount starts to increase after the second voltage is input to the controller.

(1-4) In addition to the arrangement (1-3) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution.

In the present teaching, a delay time from a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor may be, for example, a time from a time point at which the signal of the upstream oxygen sensor becomes at a reference value to a time point at which the signal of the downstream oxygen sensor becomes at the reference value. When the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors, the reference value may be, for example, a value equidistant from the first voltage and the second voltage or may be the second voltage.

(1-5) In addition to the arrangement (1-3) or (1-4) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller is configured to execute a deterioration determination process of determining whether the three-way catalyst has been deteriorated based on both the signal of the upstream oxygen sensor while the second feedback control is in execution and the signal of the downstream oxygen sensor while the second feedback control is in execution.

With this arrangement, the detachment determination process can be performed while the deterioration determination process is performed. It is therefore possible to keep the frequency of executing a feedback control different from the normal feedback control to be more or less identical with the frequency in a straddled vehicle on which a controller performing only the deterioration determination process and not performing the detachment determination process is mounted.

The controller may determine, in the deterioration determination process, whether the three-way catalyst has been deteriorated based on a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution.

(1-6) In addition to the arrangement (1-3) or (1-4) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The feedback control includes third feedback control that is different from both the first feedback control and the second feedback control. The controller is configured to execute a deterioration determination process of determining whether the three-way catalyst has been deteriorated based on both the signal of the upstream oxygen sensor while the third feedback control is in execution and the signal of the downstream oxygen sensor while the third feedback control is in execution.

With this arrangement, the precision of determination in the detachment determination process can be easily improved as compared to a case where the signal of the upstream oxygen sensor and the signal of the downstream oxygen sensor while the second feedback control is in execution are used for the deterioration determination process.

The third feedback control is different from the first feedback control in terms of the cycle and/or amplitude of increase and decrease of the fuel supply amount. The first and third feedback controls may be different from each other in terms of both the cycle and amplitude, only in terms of the cycle, or only in terms of the amplitude. When the first and third feedback control are different in terms of the cycle of increase and decrease of the fuel supply amount, the cycle of increase and decrease of the fuel supply amount in the third feedback control is longer than the cycle of increase and decrease of the fuel amount in the first feedback control. When the first and third feedback control are different in terms of the amplitude, the amplitude of increase and decrease of the fuel supply amount in the third feedback control is larger than the amplitude of increase and decrease of the fuel supply amount in the first feedback control.

The second feedback control is different from the third feedback control in terms of the cycle and/or amplitude of increase and decrease of the fuel supply amount. The second and third feedback controls may be different from each other in terms of both the cycle and amplitude, only in terms of the cycle, or only in terms of the amplitude. When the second and third feedback control are different in terms of the cycle of increase and decrease of the fuel supply amount, the cycle of increase and decrease of the fuel supply amount in the second feedback control may be longer than or shorter than the cycle of increase and decrease of the fuel amount in the third feedback control. When the second and third feedback control are different in terms of the amplitude of increase and decrease of the fuel supply amount, the amplitude of increase and decrease of the fuel supply amount in the second feedback control may be larger than or smaller than the amplitude of increase and decrease of the fuel amount in the third feedback control. When the downstream oxygen sensor is an O2 sensor, in the third feedback control, the controller controls the fuel supply amount supplied to the combustion chamber so that a change of the signal of the downstream oxygen sensor occurs. To be more specific, the fuel supply amount is controlled so that the cycle and/or amplitude of increase and decrease of the fuel supply amount is longer than the cycle and/or amplitude in the first feedback control.

The controller may determine, in the deterioration determination process, whether the three-way catalyst has been deteriorated based on a delay time of a change of a signal of the downstream oxygen sensor while the third feedback control is in execution from a change of a signal of the upstream oxygen sensor while the third feedback control is in execution.

(1-7) In addition to any one of the arrangements (1-3) to (1-6) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on a comparison between a threshold and a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution.

For example, the controller may determine that the three-way catalyst has been detached when the delay time is smaller than the threshold. The threshold may be constant or may be changed in accordance with the driving condition of the engine.

When the controller is arranged to perform the deterioration determination process and the feedback control for performing the deterioration determination process is the second feedback control, the controller may determine, also in the deterioration determination process, whether the three-way catalyst has been deteriorated based on a comparison between a threshold and a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution. In this case, the threshold in the detachment determination process is set at a value different from the threshold in the deterioration determination process.

When the controller is arranged to perform the deterioration determination process and the feedback control for performing the deterioration determination process is the third feedback control, the controller may determine whether the three-way catalyst has been deteriorated based on a comparison between a threshold and a delay time of a change of a signal of the downstream oxygen sensor while the third feedback control is in execution from a change of a signal of the upstream oxygen sensor while the third feedback control is in execution.

(1-8) In addition to any one of the arrangements (1-3) to (1-6) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on a comparison between a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution and a delay time of a change of a signal of the downstream oxygen sensor while the second feedback control is in execution from a change of a signal of the upstream oxygen sensor while the second feedback control is in execution, which is prior to the current detachment determination process.

For example, the controller may determine that the three-way catalyst has been detached when the delay time while the current second feedback control is in execution is shorter than the delay time while the past second feedback control is in execution and the difference between the delay times is larger than a reference value. The delay time in the past second feedback control that is the target of comparison may be calculated from plural delay times. For example, an average of plural delay times may be used. To be more specific, for example, an average of delay times detected during plural driving cycles may be used. Each driving cycle is a period from the start to stop of the engine. The reference value may be constant or may be changed in accordance with the driving condition of the engine.

(1-9) In addition to the arrangement (1-2) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller is configured to perform feedback control of controlling a fuel supply amount supplied to the combustion chamber based on the signal of the upstream oxygen sensor. The controller executes a detachment determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the normal feedback control is in execution. Because the arrangements described above increase the opportunities to execute the detachment determination process, it is possible to swiftly detects that the three-way catalyst is detached.

(1-10) In addition to the arrangement (1-9) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

When the signal of the downstream oxygen sensor is changed while the normal feedback control is in execution, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst has been detached based on a delay time of a change of the signal of the downstream oxygen sensor from a change of the signal input as the signal of the upstream oxygen sensor while the normal feedback control is in execution.

In the present invention, a delay time from a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor may be, for example, a time from a time point at which the signal of the upstream oxygen sensor becomes at a reference value to a time point at which the signal of the downstream oxygen sensor becomes at the reference value. When the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors, the reference value may be, for example, a value equidistant from the first voltage and the second voltage or may be the second voltage.

(1-11) In addition to the arrangement (1-10) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on a comparison between a threshold and a delay time of a change of a signal of the downstream oxygen sensor while the normal feedback control is in execution from a change of a signal of the upstream oxygen sensor while the normal feedback control is in execution.

For example, the controller may determine that the three-way catalyst has been detached when the delay time is smaller than the threshold. The threshold may be constant or may be changed in accordance with the driving condition of the engine.

(1-12) In addition to the arrangement (1-10) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller determines, in the detachment determination process, whether the three-way catalyst has been detached based on a comparison between a delay time of a change of a signal of the downstream oxygen sensor while the normal feedback control is in execution from a change of a signal of the upstream oxygen sensor while the normal feedback control is in execution and a delay time of a change of a signal of the downstream oxygen sensor while the normal feedback control is in execution from a change of a signal of the upstream oxygen sensor while the normal feedback control is in execution, which is prior to the current detachment determination process.

For example, the controller may determine that the three-way catalyst has been detached when the delay time while the current normal feedback control is in execution is shorter than the delay time while the past normal feedback control is in execution and the difference between the delay times is larger than a reference value. The delay time while the past feedback control is in execution, which is a target of comparison, may be calculated from plural delay times. For example, an average of plural delay times may be used. To be more specific, for example, an average of delay times detected during plural driving cycles may be used. Each driving cycle is a period from the start to stop of the engine. The reference value may be constant or may be changed in accordance with the driving condition of the engine.

(1-13) In addition to the arrangement (1-9) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

In the detachment determination process, the controller is configured to determine whether the three-way catalyst has been detached based on the number of changes of the signal of the upstream oxygen sensor during a first time period in which the normal feedback control is in execution and the number of changes of the signal of the downstream oxygen sensor during the first time period in which the normal feedback control is in execution.

The number of changes of the signal of the upstream oxygen sensor during the first time period may be, for example, the number of times when the signal of the downstream oxygen sensor becomes at the second voltage during the first time period or the number of times when the signal of the upstream oxygen sensor becomes at a value equidistant from the first voltage and the second voltage during the first time period. The number of changes of the signal of the downstream oxygen sensor during the first time period may be, for example, the number of times when the signal of the downstream oxygen sensor becomes at the second voltage during the first time period or the number of times when the signal of the downstream oxygen sensor becomes at a value equidistant from the first voltage and the second voltage during the first time period. The first time period may be, for example, a period of several seconds or a period from the start of the engine to the current time.

For example, the controller may determine that the three-way catalyst has been detached when the number of changes of the signal of the upstream oxygen sensor during the first time period in which the normal feedback control is in execution is larger than a first threshold and the number of changes of the signal of the downstream oxygen sensor during the first time period in which the normal feedback control is in execution is larger than a second threshold. The first threshold is larger than the second threshold. The first threshold may be constant or may be changed in accordance with the driving condition of the engine. The second threshold may be constant or may be changed in accordance with the driving condition of the engine. Instead of comparing the number of changes of the signal of the oxygen sensor during the first time period with the threshold, the number of changes per unit time of the signal of the oxygen sensor during the first time period may be compared with the threshold.

(1-14) In addition to the arrangement (1-2) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

The controller is configured to perform feedback control of controlling a fuel supply amount supplied to the combustion chamber based on the signal of the upstream oxygen sensor.

The controller executes fuel cut control of temporarily stopping supply of fuel to the combustion chamber. When the normal feedback control shifts to the fuel cut control, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst has been detached based on a delay time of a change of the signal of the downstream oxygen sensor while the fuel cut control is in execution from a change of the signal of the upstream oxygen sensor while the normal feedback control or the fuel cut control is in execution.

In the present invention, a delay time from a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor may be, for example, a time from a time point at which the signal of the upstream oxygen sensor becomes at a reference value to a time point at which the signal of the downstream oxygen sensor becomes at the reference value. When the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors, the reference value may be, for example, a value equidistant from the first voltage and the second voltage or may be the second voltage.

(1-15) A straddled vehicle of an embodiment of the first invention may be arranged as described below.

The controller is configured to perform feedback control of controlling a fuel supply amount supplied to the combustion chamber based on the signal of the upstream oxygen sensor. The controller executes fuel cut control of cutting fuel supplied to the combustion chamber. When the normal feedback control shifts to the fuel cut control, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst has been detached based on a delay time of a change of the signal of the downstream oxygen sensor while the fuel cut control is in execution from a start time of the fuel cut control.

The delay time of a change of the signal of the downstream oxygen sensor from the start time of the fuel cut control may be, for example, a time from the start of the fuel cut control to a moment when the signal of the downstream oxygen sensor becomes at a reference value. When the downstream oxygen sensor is an O2 sensor, the reference value may be, for example, a value equidistant from the first voltage and the second voltage or may be the second voltage.

(1-16) A straddled vehicle of an embodiment of the first invention may be arranged as described below.

When the downstream oxygen sensor is detached from the straddled vehicle, in the detachment determination process, the controller determines that the three-way catalyst is detached based on a signal input as a signal of the downstream oxygen sensor.

The signal input to the controller as a signal of the downstream oxygen sensor when the downstream oxygen sensor is detached is different from a signal input to the controller as a signal of the downstream oxygen sensor when the downstream oxygen sensor is not detached. When the downstream oxygen sensor is an O2 sensor, a signal that is at neither the first voltage nor the second voltage is input to the controller.

The straddled vehicle includes an exhauster connected to the engine. The exhauster may be arranged so that, when the three-way catalyst is detached from the straddled vehicle, the downstream oxygen sensor is detached together with the three-way catalyst. In such a case, when the downstream oxygen sensor is detached, the three-way catalyst is assumed to be detached, too.

(1-17) In addition to the arrangement (1-15) or (1-16) above, the straddled vehicle of the embodiment of the first invention may be arranged as described below.

In the detachment determination process, the controller is configured to determine whether the three-way catalyst has been detached based on the signal input as the signal of the downstream oxygen sensor, without using a signal input as a signal of the upstream oxygen sensor.

(2-1) The straddled vehicle of the second invention is arranged as described below.

The straddled vehicle comprises: an engine which includes a combustion chamber; a three-way catalyst which is configured to purify exhaust gas exhausted from the combustion chamber; an upstream oxygen sensor which is provided upstream of the three-way catalyst in a flow direction of the exhaust gas and is configured to detect oxygen concentration in the exhaust gas; and a controller which is configured to execute a detachment determination process of determining whether the three-way catalyst has been detached based on a signal input as a signal of the upstream oxygen sensor.

In this specification, the signal input as the signal of the upstream oxygen sensor may be an actual signal of the upstream oxygen sensor input to the controller when the upstream oxygen sensor is connected to the controller. Alternatively, the signal may be a signal input to the controller as a signal of the upstream oxygen sensor when the upstream oxygen sensor is not connected to the controller because, for example, the upstream oxygen sensor is detached or disconnection has occurred between the upstream oxygen sensor and the controller.

In the specification, a phrase “determination based on a signal input as a signal of the upstream oxygen sensor” does not exclude determination based on both a signal of the upstream oxygen sensor and a signal of the upstream oxygen sensor. The same applies to a phrase “determination based on a signal of the upstream oxygen sensor”.

In the second invention, the upstream oxygen sensor may be an O2 sensor or an A/F sensor. In the second invention, the downstream oxygen sensor may be an O2 sensor or an A/F sensor. The O2 sensor and the A/F sensor have already been detailed above.

(2-2) The straddled vehicle of an embodiment of the second invention may be arranged as described below.

When the upstream oxygen sensor is detached from the straddled vehicle, in the detachment determination process, the controller determines that the three-way catalyst is detached based on a signal input as a signal of the upstream oxygen sensor.

The signal input to the controller as a signal of the upstream oxygen sensor when the upstream oxygen sensor is detached is different from a signal input to the controller as a signal of the upstream oxygen sensor when the upstream oxygen sensor is not detached. When the upstream oxygen sensor is an O2 sensor, a signal that is at neither the first voltage nor the second voltage is input to the controller.

The straddled vehicle includes an exhauster connected to the engine. The exhauster may be arranged so that, when the three-way catalyst is detached from the straddled vehicle, the upstream oxygen sensor is detached together with the three-way catalyst. In such a case, when the upstream oxygen sensor is detached, the three-way catalyst is assumed to be detached, too.

(2-3) In addition to the arrangement (2-1) or (2-2) above, the straddled vehicle of the embodiment of the second invention may be arranged as described below.

The straddled vehicle includes a downstream oxygen sensor which is provided downstream of the three-way catalyst in the flow direction of the exhaust gas and is configured to detect oxygen concentration in the exhaust gas. In the detachment determination process, the controller is configured to determine whether the three-way catalyst has been detached based on the signal input as the signal of the upstream oxygen sensor, without using a signal input as a signal of the downstream oxygen sensor.

(3-1) The straddled vehicle of the third invention may be arranged as described below.

The straddled vehicle comprises: an engine which includes a combustion chamber; a three-way catalyst which is configured to purify exhaust gas exhausted from the combustion chamber; at least one oxygen sensor which is provided upstream and/or downstream of the three-way catalyst in a flow direction of the exhaust gas and is configured to detect oxygen concentration in the exhaust gas; and a controller which is configured to execute a detachment determination process of determining whether the three-way catalyst has been detached based on a signal of a detection unit different from the at least one oxygen sensor.

With this arrangement, when the three-way catalyst is detached, it is possible in the detachment determination process to determine that the three-way catalyst is detached, even if at least one oxygen sensor is detached.

(3-2) The straddled vehicle of an embodiment of the third invention may be arranged as described below.

The detection unit is a sensor that is used for a process or control different from the detachment determination process.

The detection unit used for a process or control different from the detachment determination process is often a sensor included in a typical straddled vehicle. It is therefore possible to perform the detachment determination process with high precision, without needing a new detection unit for the detachment determination process. The detection unit used for a process or control different from the detachment determination process may be an intake pressure sensor.

(3-3) The straddled vehicle of an embodiment of the third invention may be arranged as described below.

The detection unit is a sensor exclusively used for the detachment determination process.

The detection unit exclusively used for the detachment determination process is often a sensor not included in a typical straddled vehicle. It is therefore possible to further reliably perform the detachment determination process with high precision. The detection unit exclusively used for the detachment determination process may be, for example, a camera which is configured to read a QR code provided on an outer surface of a unit that is detached together with the catalyst. A barcode may be provided in place of the QR code and a line sensor may be provided in place of the camera.

In the third invention, the detection unit may be an exhaust gas temperature sensor configured to detect the temperature of the exhaust gas, for example. The exhaust gas temperature sensor may be provided downstream or upstream of the three-way catalyst in a flow direction of the exhaust gas. The exhaust gas temperature sensor may be used exclusively for the detachment determination process, or may be used for a process or control different from the detachment determination process.

In the third invention, the detection unit may be an exhaust gas pressure sensor configured to detect the pressure of the exhaust gas, for example. The exhaust gas pressure sensor may be provided downstream or upstream of the three-way catalyst in a flow direction of the exhaust gas. The exhaust gas pressure sensor may be used exclusively for the detachment determination process, or may be used for a process or control different from the detachment determination process.

In the detachment determination process of the first invention, at least two of the above-described determination conditions may be combined. For example, the controller does not determine that the three-way catalyst has been detached when only one determination condition is satisfied, and determines that the three-way catalyst has been detached when two or more determination conditions are satisfied. For example, the above-described arrangement (1-12) may be combined with the above-described arrangement (1-13).

In the detachment determination process of the third invention, the above-described arrangement (3-2) and the above-described arrangement (3-3) may be combined.

The controller may perform a detachment determination process in which the detachment determination process of the first invention is combined with the detachment determination process of the second invention. For example, the above-described arrangement (1-16) may be combined with the above-described arrangement (2-2). The controller may perform a detachment determination process in which the detachment determination process of the first invention is combined with the detachment determination process of the third invention. The controller may perform a detachment determination process in which the detachment determination process of the second invention is combined with the detachment determination process of the third invention.

In the present invention, the straddled vehicle includes a motorcycle, a motor tricycle, a four-wheeled buggy (ATV: All Terrain Vehicle), a snowmobile, a personal watercraft, and the like. The motorcycle encompasses a scooter. The straddled vehicle of the present invention may include at least one front wheel and at least one rear wheel. The driving wheel driven by a power source may be the front wheel, the rear wheel or both the front wheel and the rear wheel. As a power source (driving source) for generating power for running, the straddled vehicle of the present invention may include an electric motor in addition to the engine. When the straddled vehicle of the present invention includes the electric motor as the power source, the electric motor may be or may not be am in-wheel motor.

The straddled vehicle of the present invention may include a muffler (silencer). The three-way catalyst of the present invention may be provided upstream of the muffler in the flow direction of exhaust gas, or may be provided inside the muffler.

The straddled vehicle of the present invention may include plural catalysts including the three-way catalyst that is a target of the detachment determination process. Another catalyst, however, is not provided between the upstream oxygen sensor and the three-way catalyst that is a target of the detachment determination process. When the straddled vehicle of the present invention includes a downstream oxygen sensor, plural catalysts including the three-way catalyst that is a target of the detachment determination process may be provided between an upstream oxygen sensor and the downstream oxygen sensor. Another catalyst, however, is not provided between the upstream oxygen sensor and the three-way catalyst that is a target of the detachment determination process. In the present invention, a catalyst different from the three-way catalyst that is a target of the detachment determination process may be provided upstream of the upstream oxygen sensor. In the present invention, a catalyst different from the three-way catalyst that is a target of the detachment determination process may be provided downstream of the downstream oxygen sensor. When the straddled vehicle of the present invention includes plural three-way catalysts, the three-way catalyst that is a target of the detachment determination process may or may not be a main three-way catalyst which contributes to the purification of the exhaust gas most among the plural three-way catalysts.

The straddled vehicle of the present invention may include a transmission by which power generated by the engine is transmitted.

The transmission is able to transmit the power with a variable rotation speed and torque. The transmission may be a continuously variable transmission or a multistage transmission. The continuously variable transmission may be an electronic-controlled continuously variable transmission (ECVT) or a mechanical continuously variable transmission. In the present invention, the transmission may or may not be a manual transmission. The transmission may or may not be a fully automatic transmission. The transmission may or may not be a semi-automatic transmission. In a case of the manual transmission, the rider manually operates the clutch and switches the gear position. In a case of the fully automatic transmission, gear change is automatically performed in accordance with, for example, the vehicle speed and the engine rotation speed. In a case of the semi-automatic transmission, the clutch is automatically operated whereas the rider manually switches the gear position.

In the present invention, the engine may be a single-cylinder engine having one combustion chamber or a multi-cylinder engine having plural combustion chambers.

In the present invention, the fuel may be gasoline or a mixture of gasoline and alcohol.

In the present invention, the engine may be a four-stroke engine or a two-stroke engine. The four-stroke engine is suitable for the present invention as compared to the two-stroke engine.

In the present invention, the engine may include a spark plug which is configured to ignite air-fuel mixture in a combustion chamber.

In the present invention, the engine may include a throttle valve which is configured to adjust an amount of air supplied to a combustion chamber. The throttle valve may be an electronic-controlled throttle valve controlled by the controller or a mechanical-controlled throttle valve. The opening degree of the electronic-controlled throttle valve is basically controlled by the controller in accordance with an operation by the rider. The opening degree of the electronic-controlled throttle valve may be controlled by the controller without an operation by the rider. The opening degree of the mechanical-controlled throttle valve is controlled by an operation by the rider.

In the present invention, when the engine is a multi-cylinder engine, a throttle valve may be provided for each combustion chamber. This arrangement is suitable for the present invention as compared to an arrangement in which one throttle valve is provided for plural combustion chambers.

In the present invention, the engine may include a fuel injector which is configured to inject fuel into an intake passage member connected to a combustion chamber. This arrangement is suitable for the present invention as compared to an arrangement in which a fuel injector configured to inject fuel is provided in a combustion chamber.

When the engine of the present invention is a four-stroke engine, the engine includes an intake valve configured to open and close an intake port formed in a combustion chamber and an exhaust valve configured to open and close an exhaust port formed in a combustion chamber. In the present invention, the engine may include a variable valve timing mechanism which is configured to change timings to open and close an intake valve and/or an exhaust valve. The variable valve timing mechanism may be arranged so that, in at least part of a driving range, part of an open valve period of the intake valve may overlap part of an open valve period of the exhaust valve. The engine of the present invention may not include the variable valve timing mechanism, and timings to open and close the intake valve and the exhaust valve may be constant. When the variable valve timing mechanism cannot be provided, the engine of the present invention may be arranged so that part of an open valve period of the intake valve overlaps part of an open valve period of the exhaust valve. The period in which the valve open periods overlap each other is termed a valve overlap period. With the valve overlap period, it is possible to increase the output of the engine. The valve overlap period of the straddled vehicle tends to be typically longer than that of an automobile. Furthermore, the engine rotation speed range of the straddled vehicle tends to be typically wider than the engine rotation speed range of an automobile. Furthermore, the load range of the straddled vehicle tends to be typically wider than the load range of an automobile. As such, the driving range of the straddled vehicle tends to be typically wider than the driving range of an automobile. On this account, when the straddled vehicle has the variable valve timing mechanism, the driving range in which the valve opening periods overlap each other tends to be wide as compared to an automobile.

In the present invention, the engine may be an auxiliary chamber engine having a combustion chamber including a main chamber and an auxiliary chamber. In the present invention, the engine may not be an auxiliary chamber engine.

The straddled vehicle of the present invention may or may not include a forced induction device which is configured to pressurize air in order to supply the pressurized air to a combustion chamber. The forced induction device may be a mechanical supercharger, a motor-driven supercharger, or a turbocharger.

In the description, at least one of plural options encompasses all conceivable combinations of the options. At least one of plural options may be one of the options, some of the options, or all of the options. For example, at least one of A, B, or C indicates only A, only B, only C, A and B, A and C, B and C, or A, B, and C.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a straddled vehicle of First Embodiment of a first invention, a second invention, and a third invention.

FIG. 2 shows graphs for explaining Second to Seventh Embodiments of the first invention.

FIG. 3 shows graphs for explaining Eighth and Ninth Embodiments of the first invention.

DESCRIPTION OF EMBODIMENTS

The following will describe a straddled vehicle 1 of First Embodiment of the first invention, the second invention, and the third invention with reference to FIG. 1 . The straddled vehicle 1 is a motorcycle. The straddled vehicle 1 includes an engine 2 including a combustion chamber 3, an exhauster 4 connected to the engine 2, and a controller 8 performing a detachment determination process. The exhauster 4 includes a three-way catalyst 5, an upstream oxygen sensor 6 provided upstream of the three-way catalyst 5 in a flow direction of the exhaust gas, and a downstream oxygen sensor 7 provided downstream of the three-way catalyst 5 in the flow direction of the exhaust gas.

The following will describe Second Embodiment of the present invention with reference to a graph shown in FIG. 2 . In the graphs shown in FIG. 2 and later-described FIG. 3 , UpO2 indicates the upstream oxygen sensor and DnO2 indicates the downstream oxygen sensor. In Second Embodiment of the first invention, the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors. In Second Embodiment of the first invention, the feedback control for executing the detachment determination process is different from the feedback control for executing the deterioration determination process and the normal feedback control.

The graph of FIG. 2(a) shows changes over time of the fuel supply amount, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor, when the three-way catalyst is not detached and not deteriorated. The graph of FIG. 2(b) shows changes over time of the fuel supply amount, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor, when the three-way catalyst is not detached and is deteriorated. The graph of FIG. 2(c) shows changes over time of the fuel supply amount, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor, when the three-way catalyst is detached. Each of the graphs in FIG. 2(a) to FIG. 2(c) shows changes over time of the fuel supply amount, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor when three feedback controls FBα, FBβ, and FBγ are executed. The feedback control FBα is normal feedback control. In Second Embodiment of the first invention, the feedback control FBα is equivalent to first feedback control. In Second Embodiment of the first invention, the feedback control FBβ is feedback control for performing the deterioration determination process and is equivalent to the third feedback control. In Second Embodiment of the first invention, the feedback control FBγ is feedback control for performing the detachment determination process and is equivalent to the second feedback control.

The controller of Second Embodiment of the first invention determines that, in the detachment determination process, the three-way catalyst has been detached when an oxygen sensor delay time Tγ that is a delay time of a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor while the feedback control FBγ is in execution is shorter than a threshold X1. In FIG. 2 , the delay time Tγ is a time from a point at which the signal of the upstream oxygen sensor becomes equal to a value Al equidistant from a first voltage V1 and a second voltage V2 to a point at which the signal of the downstream oxygen sensor becomes equal to the value A1.

The controller of Second Embodiment of the first invention determines in the deterioration determination process that the three-way catalyst has been deteriorated, when an oxygen sensor delay time Tβ that is a delay time of a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor while the feedback control FBβ is in execution is shorter than a threshold X2. In FIG. 2 , the delay time Tβ is a time from a point at which the signal of the upstream oxygen sensor becomes equal to a value A1 equidistant from a first voltage V1 and a second voltage V2 to a point at which the signal of the downstream oxygen sensor becomes equal to the value A1. The threshold X2 may be larger than or smaller than the threshold X1, or may be equal to the threshold X1.

As shown in FIG. 2 , a difference between the oxygen sensor delay time Tα when the three-way catalyst is detached and the feedback control FBγ is in execution and the oxygen sensor delay time Tγ when the three-way catalyst is deteriorated and the feedback control FBγ is in execution is smaller than a difference between the oxygen sensor delay time TO when the three-way catalyst is detached and the feedback control FBβ is in execution and the oxygen sensor delay time Tβ when the three-way catalyst is deteriorated and the feedback control FBβ is in execution. Therefore, because the feedback control for the detachment determination process is different from the feedback control for the deterioration determination process, the precision of the detachment determination process is improved as compared to a case where the feedback control for the detachment determination process is identical with the feedback control for the deterioration determination process.

The following will describe Third and Fourth Embodiments of the first invention with reference to a graph shown in FIG. 2 . In Third and Fourth Embodiments of the first invention, the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors. In Third and Fourth Embodiments of the first invention, the feedback control for executing the detachment determination process is identical with the feedback control for executing the deterioration determination process. A controller of Third and Fourth Embodiments of the first invention executes the deterioration determination process and the detachment determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the feedback control FBβ is in execution. In Third and Fourth Embodiments of the first invention, the feedback control FBβ is equivalent to the second feedback control.

In Third Embodiment of the first invention, the controller determines in the detachment determination process that the three-way catalyst has been detached, when the delay time Tβ while the feedback control FBβ is in execution is shorter than a threshold X3. The threshold X3 is smaller than the threshold X2. The threshold X3 is equal to or smaller than the threshold X1. In the case above, the controller determines in the deterioration determination process that the three-way catalyst has been deteriorated, when the delay time Tβ while the feedback control FBβ is in execution is equal to or longer than the threshold X3 and shorter than the threshold X2. In Fourth Embodiment of the first invention, the controller determines in the detachment determination process that the three-way catalyst has been detached, when the delay time Tβ while the feedback control FBβ is in execution is shorter than an average of the oxygen sensor delay times Tβ while the feedback controls FBβ prior to the current detachment determination process are in execution and a difference between the delay time Tβ and the average is larger than a reference value Y1.

As a modification of Third and Fourth Embodiments of the first invention, the controller may execute the deterioration determination process and the detachment determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the feedback control FBγ is in execution. In this modification, the feedback control FBγ is equivalent to the second feedback control.

The following will describe Fifth to Seventh Embodiments of the first invention with reference to the graph shown in FIG. 2 . In Fifth to Seventh Embodiments of the first invention, the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors. In Fifth to Seventh Embodiments of the first invention, the controller executes a detachment determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the feedback control FBα that is the normal feedback control is in execution.

In Fifth Embodiment of the first invention, the controller determines in the detachment determination process that the three-way catalyst has been detached, when the delay time Tα while the feedback control FBα is in execution is shorter than a threshold X4. The threshold X4 is smaller than the threshold X2. The threshold X4 is equal to or smaller than the threshold X1. The threshold X4 is equal to or smaller than the threshold X3. The threshold X1, the threshold X3, and the threshold X4 may be identical with one another. In FIG. 2 , the delay time Tα is a time from a point at which the signal of the upstream oxygen sensor becomes equal to a value A1 equidistant from a first voltage V1 and a second voltage V2 to a point at which the signal of the downstream oxygen sensor becomes equal to the value A1.

In Sixth Embodiment of the first invention, the controller determines in the detachment determination process that the three-way catalyst has been detached, when the delay time Tα while the feedback control FBα is in execution is shorter than an average of the oxygen sensor delay times Ta while the feedback controls FBα prior to the current detachment determination process are in execution and a difference between the delay time Tα and the average is larger than a reference value Y2.

In Seventh Embodiment of the first invention, the controller determines, in the detachment determination process, that the three-way catalyst has been detached when the number of changes of the signal of the upstream oxygen sensor during the first time period while the feedback control FBα is in execution is larger than a threshold Z1 and the number of changes of the signal of the downstream oxygen sensor during the first time period while the feedback control FBα is in execution is larger than a threshold Z2. The first time period may be, for example, a period of several seconds. The number of changes of the signal of the upstream oxygen sensor during the first time period may be, for example, the number of times when the signal of the upstream oxygen sensor becomes at the second voltage V2 during the first time period, or the number of times when the signal of the upstream oxygen sensor becomes at the value A1. The number of changes of the signal of the downstream oxygen sensor during the first time period may be, for example, the number of times when the signal of the downstream oxygen sensor becomes at the second voltage V2 during the first time period, or the number of times when the signal of the downstream oxygen sensor becomes at the value A1. As shown in FIG. 2 , the number of changes of the signal of the downstream oxygen sensor while the feedback control FBα is in execution when the three-way catalyst is detached tends to be larger than the number of changes of the signal of the downstream oxygen sensor while the feedback control FBα is in execution when the three-way catalyst is deteriorated. On this account, it is less likely to mistake a case where the three-way catalyst is deteriorated for a case where the three-way catalyst is detached even through feedback control different from the normal feedback control is not performed for the detachment determination process.

In Fifth to Seventh Embodiments of the first invention, the controller may execute the deterioration determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the feedback control FBβ or the feedback control FBγ is in execution.

The following will describe Eighth and Ninth Embodiment of the first invention with reference to a graph shown in FIG. 3 . In Eighth and Ninth Embodiment of the first invention, the upstream oxygen sensor and the downstream oxygen sensor are O2 sensors. In Eighth Ninth Embodiment of the first invention, the controller executes a detachment determination process based on a signal of the downstream oxygen sensor while the feedback control FBα that is the normal feedback control is in execution. In Eighth and Ninth Embodiments of the first invention, the controller executes the detachment determination process by utilizing fuel cut control.

The graph of FIG. 3(a) shows changes over time of a flag of the fuel cut control, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor when the three-way catalyst is not detached. The graph of FIG. 3(b) shows changes over time of a flag of the fuel cut control, a signal of the upstream oxygen sensor, and a signal of the downstream oxygen sensor when the three-way catalyst is detached. Each of the graphs in FIG. 3(a) and FIG. 3(b) shows changes over time of a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor when the feedback control FBα is shifted to the fuel cut control.

In Eighth Embodiment of the first invention, the controller determines that the three-way catalyst has been detached when a delay time Tψ that is a delay time of a change of a signal of the downstream oxygen sensor from a change of a signal of the upstream oxygen sensor when the feedback control FBα shifts to the fuel cut control is shorter than a threshold X5. In FIG. 3 , the delay time Tψ is a time from a point at which the signal of the upstream oxygen sensor becomes equal to a value A1 equidistant from a first voltage V1 and a second voltage V2 to a point at which the signal of the downstream oxygen sensor becomes equal to the value A1. To be more specific, the delay time Tψ is a time from a point at which the signal of the upstream oxygen sensor becomes equal to the value A1 immediately before the signal becomes constant at the second voltage V2 to a point at which the signal of the downstream oxygen sensor becomes equal to the value A1. While in FIG. 3(a) and FIG. 3(b) the signal of the upstream oxygen sensor becomes equal to the value A1 during the fuel cut control, the signal of the upstream oxygen sensor may become equal to the value A1 during the feedback control FBα.

In Eighth Embodiment of the first invention, the controller determines that the three-way catalyst has been detached when a delay time Tω that is a delay time of a change of a signal of the downstream oxygen sensor from a start time of the fuel cut control is shorter than a threshold X6. In FIG. 3 , the delay time Tω is a time from the start of the fuel cut control to a time point at which the signal of the downstream oxygen sensor becomes equal to a value A1 which is equidistant from the first voltage V1 and the second voltage V2.

In Eight and Ninth Embodiments of the first invention, the controller may execute the deterioration determination process based on a signal of the upstream oxygen sensor and a signal of the downstream oxygen sensor while the feedback control FBβ or the feedback control FBγ is in execution. 

1. A straddled vehicle comprising: an engine, which includes a combustion chamber; a three-way catalyst, which is configured to purify exhaust gas exhausted from the combustion chamber; an upstream oxygen sensor, which is provided upstream of the three-way catalyst in a flow direction of the exhaust gas, and is configured to detect an oxygen concentration in the exhaust gas; a downstream oxygen sensor, which is provided downstream of the three-way catalyst in the flow direction of the exhaust gas, and is configured to detect the oxygen concentration in the exhaust gas; and a controller, which includes: a processor, and a non-transitory storage medium containing program instructions, execution of which by the processor causes the controller to execute a detachment determination process of determining whether the three-way catalyst is detached at least based on a signal input as a signal of the downstream oxygen sensor.
 2. The straddled vehicle according to claim 1, wherein, in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached based on both a signal input as a signal of the upstream oxygen sensor and the signal input as the signal of the downstream oxygen sensor.
 3. The straddled vehicle according to claim 2, wherein the controller is configured to perform feedback control of controlling a fuel amount supplied to the combustion chamber based on the signal input as the signal of the upstream oxygen sensor, the fuel amount increasing and decreasing with a cycle and an amplitude, the feedback control includes a first feedback control and a second feedback control, the cycle of the fuel amount in the second feedback control being longer than the cycle in the first feedback control, and/or the amplitude of the fuel amount in the second feedback control being larger than the amplitude in the first feedback control, and in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached based on both the signal input as the signal of the upstream oxygen sensor and the signal input as the signal of the downstream oxygen sensor, while the second feedback control is in execution.
 4. The straddled vehicle according to claim 3, wherein, in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached based on an oxygen sensor delay time while the second feedback control is in execution, the oxygen sensor delay time being a time difference between a change of the signal input as the signal of the downstream oxygen sensor and a change of the signal input as the signal of the upstream oxygen sensor.
 5. The straddled vehicle according to claim 4, wherein, in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached by comparing the oxygen sensor delay time while the second feedback control is in execution with a threshold.
 6. The straddled vehicle according to claim 4, wherein the feedback control further includes another second feedback control that is prior to the second feedback control, and in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached by comparing the oxygen sensor delay time while the second feedback control is in execution with the oxygen sensor delay time while said another second feedback control is in execution.
 7. The straddled vehicle according to claim 3, wherein, the controller is configured to execute a deterioration determination process of determining whether the three-way catalyst is deteriorated based on both the signal input as the signal of the upstream oxygen sensor and the signal input as the signal of the downstream oxygen sensor, while the second feedback control is in execution.
 8. The straddled vehicle according to claim 3, wherein, the feedback control further includes a third feedback control, which is different from both the first feedback control and the second feedback control, and which controls the fuel amount in such a way that the cycle of the fuel amount in the third feedback control is longer than the cycle in the first feedback control, and/or the amplitude of the fuel amount in the third feedback control is larger than the amplitude in the first feedback control, and the controller is configured to execute a deterioration determination process of determining whether the three-way catalyst is deteriorated based on both the signal input as the signal of the upstream oxygen sensor and the signal input as the signal of the downstream oxygen sensor, while the third feedback control is in execution.
 9. The straddled vehicle according to claim 2, wherein, the controller is configured to perform feedback control of controlling a fuel amount supplied to the combustion chamber based on the signal input as the signal of the upstream oxygen sensor, the fuel amount increasing and decreasing with a cycle and an amplitude, the feedback control includes a first feedback control and a second feedback control, the cycle of the fuel amount in the second feedback control being longer than the cycle in the first feedback control, and/or the amplitude of the fuel amount in the second feedback control being larger than the amplitude in the first feedback control, and in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached based on both the signal input as the signal of the upstream oxygen sensor and the signal input as the signal of the downstream oxygen sensor, while the first feedback control is in execution.
 10. The straddled vehicle according to claim 9, wherein, when the signal input as the signal of the downstream oxygen sensor is changed while the first feedback control is in execution, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst is detached based on an oxygen sensor delay time while the first feedback control is in execution, the oxygen sensor delay time being a time difference between the change of the signal input as the signal of the downstream oxygen sensor and a change of the signal input as the signal of the upstream oxygen sensor.
 11. The straddled vehicle according to claim 10, wherein, in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached by comparing the oxygen sensor delay time while the first feedback control is in execution with a threshold.
 12. The straddled vehicle according to claim 10, wherein the feedback control further includes another first feedback control that is prior to the first feedback control, and in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached by comparing the oxygen sensor delay time while the first feedback control is in execution with the oxygen sensor delay time while said another first feedback control is in execution.
 13. The straddled vehicle according to claim 9, wherein, in the detachment determination process, the controller is configured to determine whether the three-way catalyst is detached based on a number of changes of the signal input as the signal of the upstream oxygen sensor during a first time period in which the first feedback control is in execution and a number of changes of the signal input as the signal of the downstream oxygen sensor during the first time period.
 14. The straddled vehicle according to claim 2, wherein, the controller is configured to perform feedback control of controlling a fuel amount supplied to the combustion chamber based on the signal input as the signal of the upstream oxygen sensor, and when the feedback control shifts to a fuel cut control in which supply of fuel to the combustion chamber is paused, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst is detached based on a time difference between a change of the signal input as the signal of the downstream oxygen sensor while the fuel cut control is in execution and a change of the signal input as the signal of the upstream oxygen sensor while the feedback control or the fuel cut control is in execution.
 15. The straddled vehicle according to claim 1, wherein, the controller is configured to perform feedback control of controlling a fuel amount supplied to the combustion chamber based on the signal input as the signal of the upstream oxygen sensor, and when the feedback control shifts to a fuel cut control in which supply of fuel to the combustion chamber is paused, the controller is configured to execute the detachment determination process of determining whether the three-way catalyst is detached based on a time difference between a change of the signal input as the signal of the downstream oxygen sensor while the fuel cut control is in execution and a start of the fuel cut control.
 16. The straddled vehicle according to claim 2, wherein, the controller is configured to determine, in the detachment determination process, that the three-way catalyst is detached, when the signal that is input as the signal of the upstream oxygen sensor is a signal that is input when the upstream oxygen sensor is detached from the straddled vehicle and the signal that is input as the signal of the downstream oxygen sensor is a signal that is input when the downstream oxygen sensor is detached from the straddled vehicle.
 17. The straddled vehicle according to claim 1, wherein, in the detachment determination process, the controller is configured to determine that the three-way catalyst is detached when the signal input as the signal of the downstream oxygen sensor is a signal that is input when the downstream oxygen sensor is detached from the straddled vehicle. 